Despite classical studies and varied investigations of the past decade, knowledge of the anatomy of the inner ear in lower vertebrates is sharply limited. The lack of information concerning circumscribed taxonomic assembleges presents problems in the design and/or interpretation of functional studies, and has allowed the development of only extremely generalized concepts of the evolution of auditory structures. Thus, as a continuation and expansion of studies in progress, the primary objective of the research proposed is to contribute to the body of scientific information concerning the comparative anatomy (morphology, histology and cytology) and evolution of the vertebrate inner ear by utilizing current techniques of light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The major thrust of the work will continue to be directed toward representatives of the Reptilia, since that diversified group has been shown to be of particular interest relative to aural anatomy and evolution, but some correlated studies will also be undertaken in certain bony fishes (Osteichthyes) and amphibians (Lissamphibia). In all cases the general morphology of the inner ear will be determined by dissections and light microscopy of serial sections, and fine structural investigations will treat primarily with the auditory receptors and their immediate adnexa. The findings will be evaluated by classical descriptive and comparative anatomical methods, and insofar as data are available, they will be correlated with information on the auditory capacities of the various forms utilized. Although it is not assumed that findings will be directly referable to the ear and hearing in mammals, these studies should provide a better understanding of the phylogeny and possible significance of some of the specializations of mammalian auditory receptors.